The present invention relates to a pressing diaphragm provided with a projection member which helps maintain a predetermined gap between adjacent filter plates and supports the filtering face of a pressing filter plate, and also relates to the pressing filter plate provided with the pressing diaphragm.
Various conventional compression type of filter presses are known which carrying out filtration by holding a cake between a pair of filter cloths provided between a normal filter plate and a pressing filtering plate, and compressing the cake by expanding the pressing diaphragm of the pressing filter plate. According to one compression type of filter press (Japanese Utility Model Publication No. 56-11928), in mounting the pressing diaphragm on the pressing filter plate, a circular metallic plate is provided in the center of the pressing diaphragm and the metallic plate is fixed to the main body of the pressing filter plate with bolts.
According to the above-described construction, since the pressing diaphragm is fixed to the filter plate with the circular metallic plate, a load concentrates on the pressing diaphragm in the periphery of the circular metallic plate with the expansion of the pressing diaphragm, and as a result, the pressing diaphragm at the periphery of the metallic plate is likely to be damaged, i.e. is likely to crack.
Additionally, according to the above-described construction, the pressing diaphragm being fixed to a filter plate only by the above circular metallic plate can be compared to a large rubber film being held fixed by a small pin. When the rubber film expands in such a condition, a load concentrates on the film in the periphery of the pin. That is, with the expansion of the pressing diaphragm a load concentrates on the pressing diaphragm at the entire periphery of the circular metallic plate, and as a result, the pressing diaphragm at the periphery of the metallic plate is likely to be damaged, i.e. is like to crack.